This invention relates generally to seat belts for seat occupants and more particularly concerns a seat belt retractor system designed for use in automobiles or other conveyances and one that utilizes a simplified motorized drive arrangement for the purpose of removing slack in the seat belt and providing tensioning of the seat belt in an emergency situation.
There have been various disclosures of seat belt retractors that incorporate motors which serve to remove slack in the seat belt as well provide tensioning of the seat belt under an emergency situation. One example of such seat belt retractor can be seen in European Patent Application EP 0800970A1 to Takata Corporation. This patent discloses a seat belt retractor that has an ultrasonic motor integrated with a belt reel of the retractor. There is no gear or clutch between the motor and reel and, instead, the shaft of the reel is directly connected to a plurality of piezoelectric devices which flex in a wave-like manner under the influence of ultrasonic signals for drivingly rotating the reel in one direction or the other. Other forms of retractors which have been proposed by others have the shaft of an electric motor connected to the reel through a planetary gear arrangement or through a worm gear arrangement.
The problem with a direct drive ultrasonic motor for use with a seat belt retractor is that the overall mechanism becomes an expensive piece of hardware which lacks reliability and makes serviceability more difficult. As to the motorized drives that are connected to the reel through a planetary gear arrangement, it has been found that such an arrangement may need a clutch, tends to have weak reeling power, and is quite noisy when operating. The worm gear arrangement similarly may require a clutch to operate properly and has also been found to suffer from the same noise problem encountered with the planetary gear arrangements.
Accordingly, there has been a need to provide a seat belt retractor system for removing slack and providing tensioning of the seat belt in an emergency situation that is cheaper in construction, quieter in operation, more reliable, and one that can be serviced easily.
To this end, one object of the present invention is to provide a new and improved seat belt retractor system that includes an electric motor connected through a simplified and reliable chain drive arrangement to the reel of the retractor mechanism so as to render the overall retractor mechanism quiet and less expensive to manufacture.
Another object of the present invention is to provide a new and improved seat belt retractor system that incorporates an electric motor which has its output shaft provided with a sprocket wheel that is connected through an endless chain to a sprocket wheel mounted to the input shaft of a reel supporting a seat belt.
A further object of the present invention is to provide a new and improved seat belt retractor system having an electric motor connected through a chain drive to the shaft of a reel and in which the only resistance to the initial withdrawal of the seat belt by the seat occupant is the inertia and friction of the electric motor, the chain drive, the reel, and the spooled belt.
A still further object of the present invention is to provide a new and improved seat belt retractor system incorporating an electronic control unit that serves to energize an electric motor which acts through a chain drive for automatically adjusting the tension of the seat belt to provide a predetermined seat belt loading of the seat belt onto the seat occupant.
A still further object of the present invention is to provide a new and improved seat belt retractor system having an electronic control unit which is adapted to receive a signal from a sensor responsive to the buckling of the seat belt and cause an electric motor acting through a chain drive to drivingly rotate a reel in one direction for providing a predetermined seat belt loading on the seat occupant.
A still further object of the present invention is to provide a new and improved seat belt retractor system for an automotive vehicle having an electronic control unit which is interfaced with a manual control for providing a desired tensioning of the seat belt and is also capable of receiving and continuously evaluating information about the braking of the vehicle so as to automatically increase the tension of the seat belt in emergency situations determined by the peak acceleration of the brake pedal exceeding nominally 10 g""s by rapid application of the brake pedal in an emergency and, afterwards, the removal of the belt tension is realized by exceeding a time duration, removal of the foot from the brake pedal, or if there is a change in gear of the vehicle from forward to reverse.
The above and other objects are realized in accordance with the present invention by a seat belt retractor system which, in the preferred form, has a seat belt retractor mechanism incorporated within the center pillar of an automotive vehicle adjacent a seat assembly. The seat belt retractor system is adapted to provide a predetermined seat belt loading on a seat occupant under various operating conditions of the vehicle after the seat belt is buckled.
More specifically, the seat belt retractor system according to the present invention includes the above-mentioned seat belt retractor mechanism which has a seat belt wound about a reel that is supported within the aforementioned center pillar of the vehicle. The reel is fixed to an input shaft having a sprocket wheel mounted thereon that allows the reel to rotate, permitting the seat belt to be retracted or extended. The seat belt retractor mechanism also includes an electric motor supported within the pillar below the reel that has an output shaft rigidly connected to another sprocket wheel.
An endless chain is entrained about and interconnects the two sprocket wheels. The arrangement is such that when an occupant enters the vehicle, the seat belt can be pulled by the seat occupant without having to overcome the continuous force of a spring typically found in conventional seat belt retractors. The only resistance to pulling the seat belt is created by the inertia and friction of the chain drive, electric motor, the reel, and the spooled seat belt. If the belt tension is released, the seat belt stays in position. This advantage is realized by having a control device which prevents energization of the electric motor when the seat belt is initially extended by the seat occupant. After the seat belt is buckled, a sensor responsive to the buckling of the seat belt and acting through the control device sends a signal to the electric motor to energize the electric motor and cause the input shaft to be drivingly rotated in a direction for providing a predetermined seat belt loading on the seat occupant.
In addition, an added feature of the seat belt retractor system according to the present invention is that the seat occupant can manually vary the tension of the seat belt so that differing comfort levels can be provided to the seat occupant. For example, a higher tension level can be selected for high-speed highway driving so that the seat occupant is held more securely in the seat. Another feature of the seat belt retractor system according to the present invention is the use of a sensor to measure brake pedal acceleration to indicate an emergency situation. In this regard, the control unit includes specific logic which has the seat belt loading on the seat occupant increase only when the velocity of the brake pedal exceeds a certain level and is maintained for a predetermined time period.